FIG. 1 illustrates a typical prior art implantable stimulation device. A stimulation source generates one or more electrical signals for delivery of electrical stimulation to a desired location via one or more channels or outputs. The stimulation source produces pulse generator outputs P1, P2, P3, . . . , Pn for delivery to the desired location via output terminals T1, T2, T3, . . . , Tn. As will be appreciated, the term “terminal” as used herein is not limited to an input/output terminal, and also refers to a node or other connection between two or more points or signals, whether internal or external to any integrated circuit or other discrete element(s). The stimulation signals may be applied directly from the output terminals, but are usually applied through a lead or lead extension having corresponding electrodes electrically connected to the output terminals. Any number of the n pulse generator outputs (and corresponding output terminals) may be active or operating at a given time to deliver electrical energy.
Coupling capacitors C1, C2, C3. . . , Cn are provided between each pulse generator output P1 thru Pn and each output terminal T1 thru Tn to block direct current (DC) signals (current, voltage) from being applied to the respective output terminals (and hence to the electrodes of the lead). These capacitors are physically large and require a significant amount of space. In the prior art systems, as the number of pulse generator outputs (and output terminals) operable for stimulation increases (e.g., from 4 to 8, from 8 to 16, 16 to 32, etc.), the number of coupling capacitors also increases—one for each pulse generator output (and output terminal). Increasing the number of outputs and terminals (or electrodes in the lead) allows for increased programmability and selection of stimulation patterns and stimulation points/areas. However, the increase in the number of outputs/terminals also increases the number of large coupling capacitors needed. This is undesirable, as one of the goals is reduce the size of the implantable device.
Accordingly, there is a need for an implantable stimulation device that effectively reduces the number of coupling capacitors that are utilized. In addition, there is needed a programmable switch array or matrix operable for selectively coupling a plurality of generated electrical signals to a plurality of output terminals.